Come on now, that is just ridiculous! That is EXACTLY what 6th gear is for! It's not like you will be using 6th on the track. Many 'high performance' cars as you put it, don't have drone. Exhausts can be tuned in order to avoid drone in that cruising sweet spot and still maintain high flow and an aggressive sound. This is why Eisenmann spends months on RD to get the right sound without the dreaded drone before they release it to the public for sale, while other companies just spit something out in order to sell it first.